1. Field of the Invention
The present invention relates to a wireless communication system; and more particularly, a method of making downlink operational measurements in a wireless communication system.
2. Description of Related Art
Conventional wireless communication systems include a plurality of cell sites, each having a base station sending and receiving signals over one or more associated antenna systems. Accordingly, each base station has one or more coverage areas (geographic areas in which a mobile terminal will communicate with the base station) associated therewith and collectively called a cell. The number of coverage areas associated with a base station depends on the design of the cell site including that base station. The cell site could include an omni-directional antenna system (azimuth angle of 360 degrees), and provide a single coverage area. Alternatively, the cell site could include a multi-sector antenna system and provide a number of coverage areas. For instance a three-sector antenna system (azimuth angle of 120 degrees) provides three coverage areas commonly referred to as sectors. Therefore, a single base station may transmit and receive the signals associated with more than one coverage area.
Operators of a wireless communication system monitor the quality of system performance by taking operational measurements indicative thereof. These operational measurements represent the quality of uplink communication, communication from a mobile terminal to the base station, and the quality of the downlink communication, communication from the base station to a mobile terminal. Instead of uplink and downlink, the terms reverse and forward, respectively, are common in the art. The downlink operational measurements include, but are not limited to, signal strength of a signal received from a base station, signal-to-noise or signal-to-noise plus interference ratios of signals received from a base station, bit error and frame error rates of signals received from a base station, etc.
Techniques exist, such as in mobile assisted hand-off (MAHO), for a base station to originate a request that mobile terminals in communication with the base station make some operational measurements of downlink signals received from the base station, or downlink signals received from the base station and other base stations. A mobile terminal in communication with a base station is in one of two states: (1) registered with the base station and monitoring a forward or set-up channel of the base station (e.g., a set-up channel in the Advanced Mobile Phone System, a Digital Control CHannel in the North American Time-Division Multiple Access System, the Broadcast Control Channel in the Global System for Mobiles, a paging channel in a Code-Division Multiple Access system, etc.); or (2) in an active call on a devoted traffic channel served by the base station. Accordingly, in MAHO, a base station originates a request, to mobile terminals in a coverage area associated therewith, that the mobile terminals make operational measurements of downlink signals from the base station and, perhaps, surrounding base stations as well. These measurements are then used in the hand-off determination process of MAHO.
Another conventional technique for making downlink operational measurements is referred to as drive testing. In drive testing, one or more test receiver is deployed at known measurement locations within the coverage areas of a base station, and operational measurements are made of downlink signals from that base station.
Also, many wireless communication systems include a test radio at each base station to perform a self test operation. The test radio mimics the functions of a mobile terminal to test whether the base station is transmitting and receiving signals properly.
While these techniques provide information about the downlink signals within the coverage areas of the base station of interest, the techniques do not provide information regarding the impact of the downlinks signals from one base station on the quality of system performance in coverage areas of another base station. Furthermore, existing techniques like drive testing make downlink operational measurements in a complex and costly manner.